This invention relates to a novel two-step process for isolation and purification of avermectin compounds which are produced by the microorganism, Streptomyces avermitilis. The process described herein involves two-steps, namely, crude crystallization of avermectin B1 and crude crystallization of avermectin B2 component from mother liquors obtained from a conventional process for preparation of said avermectin B1 compounds.